The present invention relates generally to automatic safety devices for pressurized tanks and more particularly relates to automatic safety devices for use with pressurized tanks of gas blast circuit breakers.
Automatic safety devices are known, for example, to protect the low pressure reserviors of gas blast circuit breakers against overpressures. Typically a gas blast circuit breaker includes a source of high pressure gas which provides compressed gas to a low pressure reservoir. To protect the low pressure reservoir against overpressures prior art safety devices, generally featuring a spring-loaded safety valve, have been attached to the low pressure reservoir. The spring-loaded safety valves then release the compressed gas from the low pressure reservior to the atmosphere in the event of an overpressure.
These prior art safety devices, however, have not been entirely satisfactory in that significant amounts of the high pressure reserve of the compressed gas are released to the atmosphere. This release is often accompanied by considerable noise. In addition, it has often been necessary to take measures to prevent environmental and weather effects from interfering with the operation of these prior art safety devices.
Accordingly, it is a primary object of the present invention to provide a safety device which will prevent overpressures from occurring in low pressure reservoirs connected to high pressure sources, particularly the low pressure reservoirs used in gas blast circuit breakers.
Another object of the present invention is to provide a safety device which protects low pressure reservoirs, connected to high pressure sources, against overpressures without producing excessive noise.
A further object of the present invention is to provide a safety device which protects low pressure reservoirs, connected to high pressure sources, against overpressures with little or no depletion of the high pressure reserve of compressed gas.
Yet another object of this invention is to provide a safety device which is substantially unaffected by icing, contamination, and other adverse weather and environmental effects.
An automatic, pressure actuated safety device for a low pressure reservoir receiving compressed gas from a high pressure source, according to the present invention, includes a cylinder in pressure communication with the low pressure reservoir. A spring-biased piston is provided within the cylinder with a toothed rack fastened to the piston projecting from a first opening in the cylinder. The safety device also includes a spherical stopcock on a feed line connecting the high pressure source to the low pressure reservoir, which stopcock has a toothed segment that is engaged by the toothed rack projecting from the cylinder. Longitudinal motion of the toothed rack urges the spherical stopcock to open or close.
A preferred embodiment of the safety device, according to the present invention, further includes a second opening in the cylinder which allows compressed gas in the cylinder to be released to the atmosphere.